Graphene supports a ratchet motion of electrons when placed in a magnetic field

(Nanowerk News) A ratchet supports one-way traffic. One can pull it back and forth, but it only moves forwards. Mechanical ratchets, used to pull or hold heavy objects, are familiar examples. Also, some electronic devices are based on ratchets. Transistors are made out of diodes, which rectify electrical currents: however hard one pushes electrons in both directions, they flow only in one. Now an international consortium consisting of research groups from Germany, Russia, Sweden, and the U.S., led by the experimental group of Prof. Dr. Sergey Ganichev from the University of Regensburg and supported by the theoretical group of Prof. Dr. Sergey Tarasenko (St. Petersburg) and Prof. Dr. Jaroslav Fabian (Regensburg), has demonstrated that electronic ratchets can be successfully scaled down to one-atom thick layers.

The researchers showed that graphene, a single layer of carbon atoms arranged in a honeycomb lattice, supports a ratchet motion of electrons when placed in a magnetic field. They applied terahertz laser fields to push the electrons back and forth, while the magnetic field acted as a valve to let only those electrons moving in one direction go on, stopping the others. The results of the research group are reported in an issue of Nature Nanotechnology ("Magnetic quantum ratchet effect in graphene").

Graphene may be the ultimate electronic material, possibly replacing silicon in electronic devices in the future. It has attracted worldwide attention from physicists, chemists, and engineers. Its discoverers, A. Geim and K. Novoselov, were awarded the physics Nobel Prize for it in 2010. The discovery of the ratchet motion in graphene greatly adds to the technological potential of this material and to the prospects of further miniaturization of electronic devices. Before carbon based electronics might take over from silicon many fundamental physical challenges need to be addressed.

In Regensburg, research activities on graphene are embedded in larger research programs, funded by the German Science Foundation (DFG). These are a PhD program on carbon based electronics (DFG-Research Training Group GRK 1570, spokesperson: Prof. Dr. Milena Grifoni) and a Collaborative Research Center (SFB 689, spokesperson: Prof. Dr. Dieter Weiss) funding more than 40 PhD students, as well as projects within a DFG Priority Programm (SPP 1459, spokesperson: Prof. Dr. Thomas Seyller, Chemnitz). The international cooperation on terahertz physics and technology is coordinated by the Regensburg Terahertz Center (TerZ, directed by Prof. Dr. Sergey Ganichev), also funded by the International Bureau of the German Ministry of Education and Research.